Report No.: 15111045 Date: 27.11.15 Engineers Report FSM 250 Roof Anchor Overview Methodology AS/NZS 1891.4:2009 Loading Anchorage Application Analysis Parameters Acceptance Criteria Results Conclusions Recommendations Appendix A Analysis Results 2,600 N Anchor Load AS/NZS 1891.4:2009 Free Fall Loading Overview BVT Engineering Professional Services has been requested by Brian Woods of Innovative Ceiling Systems to review the adequacy of using a Collins Corporation Ltd FSM 250 roof anchor with eight 14g x 25mm Tekscrews, into a 25mm wood fibre panel. The system is illustrated below in figure 1. Figure 1 FSM 250 roof anchor system The FSM 250 roof anchor is only to be treated as a Total Restraint anchor as defined by AS/NZS 1891.4:2009, as per the manufacturer s specification. The manufacturer also gives two attachment systems, which are: 1. 7.70 Olympic Bulb Tite Rivets 2. Sikaflex 11FC Adhesive The purpose of this report is to determine the adequacy of using eight 14g x 25mm Tekscrews, as opposed to either of the above arrangements. 15111045 1
Methodology AS/NZS 1891.4:2009 Loading As per Appendix F of AS/NZS 1891.4:2009, Total Restraint is defined as the control on a person s movement by means of a connection to an anchorage in such a way that it will physically prevent the person from reaching any position at which there is risk of a fall, either over an edge, through a surface or due to a failed moveable platform. Total Restraint loading is omitted from the AS/NZS 1891 series, and does not provide any advice on strengths needed for Total Restraint anchorages. It is therefore up to the user to ensure the suitability of equipment used for Total Restraint. The minimum loading requirements for fall arrest anchors are defined as follows: Limited Free Fall: Free Fall: 12 kn 15 kn Anchorage Application The manufacturer does not give a rating for the FSM 250, as it is specifically used for Total Restraint. Therefore the anchorage system must be used on roofs with a pitch less than 25 degrees, as per Best Pratcice Guidelines for Working on Roofs 2012. An illustration of a Total Restraint system is outlined in figure 2. Analysis Parameters Figure 2 Illustration of Total Restraint system Since there are no specific loading requirements for Total Restraint anchors as per AS/NZS 1891.4, a representative system will be modelled using Finite Element Analysis (FEA) to determine the loading the system can withstand. This will be the basis for determining the adequacy of the anchor strength. 15111045 2
ANSYS 15.0 Mechanical Application has been used for FEA with the following parameters: Finite Element Model: ANSYS 15.0 Static Structural Analysis Type: Solid Elements, Large Deformation Material Model: Stainless Steel (NL) Yield Strength: Fy = 210 MPa Young s Modulus: E = 193 GPa Tangent Modulus: Et = 1.8 GPa Poisson s Ratio: v = 0.31 Material Model: Wood Panel Young s Modulus: E = 6.0 GPa Poisson s Ratio: v = 0.35 Contact Model: Frictionless contact between anchor and panel The ANSYS model setup and results can be found in the Appendices. Acceptance Criteria Since the FSM 250 roof anchor is an OEM component, the acceptance criteria will focus on the validation of the anchorage fixings. NZS 3603:1993 Timber Structures has been used for guidance of fixing validation. The following limits for the Tekscrews were determined using guidance from NZS 3603: Single Shear Limit: Pullout Limit: Vf = 1,500 N Nf = 1,900 N Note that these limits are consistent with the Tekscrew catalogue, however to confirm these limits it is highly recommended that physical testing of the system is conducted. 15111045 3
Results It was calculated that the roof anchorage system was inadequate for fall arrest loading in accordance with AS/NZS 1891.4:2009. Excessive stress was present in the FSM 250 roof anchor, and the Tekscrews were well above the allowable limits. Based upon the limits of the Tekscrews outlined in this report, the roof anchorage system was found to be adequate for an unfactored ultimate load of 2,600 N. Slight yielding within the baseplate of the FSM 250 roof anchor was present, however this was not deemed to cause catastrophic failure in the system. It was apparent that the FSM 250 roof anchor had a flexible baseplate design. Figure 3 shows the stress path which tends to load only three Tekscrews within the system. It is expected that using a stiffer baseplate design, the load will be transferred across more Tekscrews. Table 1 below outlines the calculated Tekscrew loads for two load cases. Figure 3 Von Mises stress path for FSM 250 roof anchor (@ 2,600 N) Table 1 Tekscrew Shear & Pullout Loads Load Scenario Tekscrew Shear, V* Tekscrew Pullout, N* 2,600 N 1,423 N 1,868 N 15,000 N 5,841 N 3,370 N 15111045 4
Conclusions The FSM 250 roof anchor shall be used only as a Total Restraint System, as shown in figure 2. It is therefore not suitable for pitched smooth roofs exceeding 25 degrees as per the Best Practice Guidelines for Working on Roofs:2012. It can be concluded that the system shown in figure 1 is inadequate for fall arrest loading as per AS/NZS 1891.4:2009. AS/NZS 1891.4:2009 does not give strength requirements for a Total Restraint anchor, however AS/NZS 1891.4:2000 has a 6 kn requirement for Total Restraint. The 6 kn load requirement has been omitted from the latest standard, and it is up to the user to define an appropriate level on strength for a Total Restraint anchor. It is expected that the system outlined in figure 1 will withstand an unfactored ultimate load of 2,600 N. This load equates to a pulling force of 260 kg, which is deemed to be acceptable for use as a single person Total Restraint system. Compliance with the definition outlined Appendix F of AS/NZS 1891.4:2009 is required for the anchorage to be classed as a Total Restraint system. Recommendations The following is strongly recommended: Physically test the system shown in figure 1 to confirm the shear and pullout values of the Tekscrews Increase the baseplate thickness of the FSM 250 roof anchor if fall arrest compliance is required Introduce a circular bolt pattern for even load distribution and additional Tekscrews if fall arrest compliance is required Working on pitched roofs must have anchors rated for fall arrest loading Report Completed By Max Waters Engineer/Client Manager, BVT Engineering Professional Services Report Approved By Mike Walker, MIPENZ, CPeng #1002287 Engineer/Client Manager, BVT Engineering Professional Services 15111045 5
Appendix A Analysis Results 2,600 N Anchor Load Figure A1 2.6 kn load model setup Figure A2 2.6 kn load deformation (true scale) 15111045 6
Figure A3 2.6 kn load Von Mises stress (capped at yield strength) Figure A4 2.6 kn load Von Mises stress (section view) 15111045 7
AS/NZS 1891.4:2009 Free Fall Loading Figure A5 15 kn fall arrest load model setup Figure A6 15 kn fall arrest load deformation (true scale) 15111045 8
Figure A7 15 kn fall arrest load Von Mises stress (capped at yield strength) Figure A8 15 kn fall arrest load Von Mises stress (section view) 15111045 9